HOW TO DECODE THE MODEL OUTPUT STATISTICS GUIDANCE MESSAGE

INTRODUCTION

The Hydrometeorological Center of the National Environmental Prediction
Centers (formerly National Meteorological Center) produces a short
range (6 to 60 hours) MOS (Model Output Statistics) guidance package
generated from the NGM (Nested Grid Model) for over 300 individual
stations in the continental United States. These alphanumeric
messages are made available at approximately 0400 and 1600 UTC
for the 0000 and 1200 UTC forecast cycles, respectively.

To indicate snow and precipitation type forecasts, the message
varies between the cold (16 Sep through 15 May)
and warm (16 May through 15 Sep) seasons. Snow and
precipitation type forecasts are never issued for certain Florida
and California stations.

DECODING THE MESSAGE

Each line in the body of the message begins with an abbreviation
of no more than five alphanumeric characters identifying the particular
forecast sequence of the weather element appearing in that line.
These abbreviations are noted in the description of each part
of the message below:

MESSAGE HEADER

This message heading accompanies each forecast message and serves
for identification purposes:

The first line of the message includes a WMO header used for communications
purposes:

FOUS14 KWBC MMDDHH

The second line of the header includes:

STATION LOCATION IDENTIFIER

A three-letter FAA/NWS identifier is the first entry of the
second line and is used to identify the station for which the
forecast has been prepared.

NWS REGIONS:

Immediately following the station locator, a letter indicates
the NWS Regions where this message is transmitted over the AFOS
network; more than one letter indicates that the message will
appear in more than one region. The NWS Region code is:

The third and fourth lines (DAY, HOUR) are header lines for
the columns in the message text and denote the day of the month
and hour (UTC) at which these forecasts are valid ("specific
time forecasts") or the time corresponding to the end of
a particular interval, such as those intervals used for forecasting
precipitation accumulation.

MAXIMUM/MINIMUM TEMPERATURE FORECASTS: MX/MN

The anticipated maximum and minimum surface temperature forecasts
(MX/MN) are the extreme temperatures expected to occur within
consecutive 12 hour intervals. These forecasts are listed directly
under the appropriate forecast time header for 24, 36, 48 and
60 hours after the initial data time (0000 or 1200 UTC). The order
depends upon the time of the forecast production run in relation
to the local day/night cycle. For reference purposes, daytime
is defined from 0700 to 1900 Local Standard Time (LST), while
nighttime runs between 1900 and 0800 LST. Hence, the order of
the MX/MN sequence for the 0000 UTC cycle starts with the maximum
temperature for the calendar day (today), tonight's minimum, tomorrow's
maximum and tomorrow night's minimum. The sequence for the 1200
UTC cycle is tonight's minimum, tomorrow's maximum, tomorrow night's
minimum and the following day's maximum.

Each extreme temperature forecast is tabulated in whole degrees
Fahrenheit, with a maximum of three characters, thereby permitting
temperatures of 100°F or more to be included. Temperatures
below 0°F contain a minus sign. A missing forecast is indicated
by "999".

SURFACE TEMPERATURE and DEWPOINT FORECASTS:
TEMP and DEWPT

Forecasts of the surface air temperature (TEMP) and dewpoint
(DEWPT) for each specific three hour forecast time are provided
from 6 hours to 60 hours after 0000 or 1200 UTC. These forecasts,
listed on two separate lines, are in whole degrees Fahrenheit.
Temperatures below 0°F contain a minus sign. A missing forecast
is indicated by "999". Consecutive forecasts of 100°F
or more (or -10°F or less) will appear without intervening
spaces separating the forecasts.

OPAQUE CLOUD AMOUNT CATEGORICAL FORECASTS: CLDS

Specific time forecasts of opaque cloud cover categories are
made at 3 hour intervals from 6 to 60 hours following 0000 or
1200 UTC. These categorical forecasts, appearing under each forecast
time header, use the following two letter designators identifying
the best category:

SURFACE WIND DIRECTION and WIND SPEED FORECASTS:
WDIR & WSPD

Forecasts of the 1 minute-average near-surface wind direction
and wind speed at the specific 3 hour forecast times are listed
starting with 6 hours after 0000 or 1200 UTC and ending at 60
hours. Each variable is listed on a separate line.

The wind direction (WDIR) forecasts are coded as two digits,
in units of tens of degrees measured clockwise from true north
(01 = 10° to 36 = 360°); calm conditions are coded "00".

The two-digit wind speed (WSPD) forecasts are given to the
nearest knot, with a maximum speed of 98 knots; calm conditions
are coded "00".

Missing WDIR and WSPD forecasts are coded as "99".

PROBABILITY OF PRECIPITATION: POP06 and POP12

The forecasts of the probability of measurable precipitation
(0.01 inch or more of liquid equivalent) occurring within a 6
or 12 hour period are included as the Probability of Precipitation
(PoP) in a 6 hour period (POP06) and Probability of Precipitation
in a 12 hour period (POP12), respectively. Two lines are employed.
The 6 hour PoPs are valid for intervals of 6-12, 12-18, 18-24,
24-30, 30-36, 36-42, 42-48, 48-54 and 54-60 hours after the initial
data times. The 12 hour PoPs are valid for intervals of 12-24,
24-36, 36-48 and 48-60 hours after the initial data times.

In the message, the PoPs are tabulated at the end time of
the noted time interval. The numeric values of the PoPs are given
to the nearest percent, ranging between 0 and 100%. A missing
forecast is indicated by "999".

QUANTITATIVE PRECIPITATION FORECASTS: QPF

The forecast of the liquid-equivalent precipitation amount
accumulated during 6 hour and 12 hour intervals are identified
as the QPF. These forecasts are displayed in the FOUS 14 message
as a categorical format with a single digit. The appropriate code
for each of the eight QPF categories appears in the accompanying
table; these categories depend upon the interval length. The QPF
forecast for a 6 hour accumulation appears to the left of the
diagonal entry at the end of each 6 hour interval corresponding
to the specific forecast times starting with 6 hours and concluding
60 hours after 0000 and 1200 UTC. The QPF code for a 12 hour period
is to the right of the diagonal appearing at 12 hour intervals
commencing with 24 hours after 0000 or 1200 UTC and ending at
60 hours.

THUNDERSTORM AND SEVERE STORM PROBABILITIES:
TSV06 and TSV12

The forecast of the probability of a thunderstorm occurring
during a 6 hour period (TSV06) are displayed to the left of the
diagonal for each 6 hour interval commencing with 6 hours and
ending with 60 hours following 0000 or 1200 UTC. A conditional
probability of severe thunderstorms during the same 6 hour interval
appears to the right of these diagonals.

Likewise, the thunderstorm probability forecasts for a 12
hour period (TSV12), together with the 12 hour conditional severe
thunderstorm probabilities, are given on a separate line, using
the same format as noted above for TSV06. The 12 hour intervals
commence with 6 hours following 0000 or 1200 UTC and end with
54 hours.

All thunderstorm and severe thunderstorm probabilities are
coded to the nearest whole percent. The thunderstorm probabilities
range from 0 to 100%, and a missing value is "999".
The range for the conditional severe thunderstorm probabilities
is from 0 to 98%, with a missing value of "99".

PRECIPITATION TYPE FORECASTS: PTYPE

The forecast of precipitation type (PTYPE), provided that
precipitation will occur, appears in the FOUS 14 message for each
specific time. This set of statistics is generated for the cold
season only. The forecast code utilizes a single letter, as found
in the following table, and is found under each forecast time
between 6 and 60 hours after 0000 and 1200 UTC.

PRECIPITATION TYPE CATEGORIES

R Liquid Rain, drizzle or a mixture of rain and snow
Z Freezing Freezing rain, freezing drizzle, ice pellets
or a combination of any of these with other
S Solid types
X Missing Snow, snow grains, snow pellets or snow
showers
Missing

PROBABILITY OF FREEZING PRECIPITATION FORECASTS: POZP

The conditional probability of freezing precipitation (POZP)
forecasts are included in the FOUS 14 message for the cold season
only. This time specific probability is based upon the condition
that precipitation occurs at that time. In this context, freezing
precipitation is defined as the occurrence of freezing rain or
drizzle, ice pellets, or any mixture of these elements with other
precipitation types. The probabilities are listed to the nearest
whole percent (with a range from 0 to 100%) for each specific
3 hour time from 6 to 60 hours after 0000 and 1200 UTC. A missing
forecast is identified by "999".

PROBABILITY OF SNOW FORECASTS: POSN

The conditional probability of snow (POSN) forecasts, based
upon the condition that precipitation occurs, are included in
the FOUS 14 message for the cold season only. In this context,
snow is limited to the occurrence of a pure snow event, to include
snow, snow showers, snow grains, snow pellets or any combination
of these elements. Snow mixed with rain is considered a liquid
precipitation event. The probabilities are listed to the nearest
whole percent (with a range from 0 to 100%) for each specific
3 hour time from 6 to 60 hours after 0000 and 1200 UTC. A missing
forecast is identified by "999".

Note: While the conditional probability of liquid precipitation
is not provided in this message, the three conditional probabilities
for freezing, frozen (snow) and liquid must add to 100%.

SNOW AMOUNT CATEGORICAL FORECASTS: SNOW

Forecasts of the amount of snow accumulated for both 6 hour
and 12 hour periods (SNOW) are included in the FOUS 14 message
for the cold season only. A set of five categories is used and
the numeric codes are listed below; these categories depend upon
the length of the period. These categorical forecasts of snow
amount for a 6 hour period appear to the left of the diagonal,
under the times commencing with 12 hours and ending with 60 hours
after 0000 or 1200 UTC. The forecasts of snow for the 12 hour
periods are found to the right of the diagonal, under the times
commencing with 24 hours and ending with 60 hours after 0000 or
1200 UTC.

SNOW AMOUNT CATEGORIES

0 no snow expected;
1 a trace to less than 2 inches;
2 2 inches or more for 6 hour forecast;
4 2 to less than 4 inches for 12 hour forecast;
unavailable for 6 hour forecast;
5 4 to less than 6 inches for 12 hour forecast;
unavailable for 6 hour forecast;
9 6 inches or more for 12 hour forecast;
no forecast available.

CEILING HEIGHT CATEGORICAL FORECASTS: CIG

Ceiling height forecasts (CIG) for each specific 3 hour forecast
time from 6 to 48 hours are made using seven categories of ceiling
height. The digital code for each forecast ceiling height category
appears in the accompanying table. These single digit forecast
codes are found under the appropriate valid time.

VISIBILITY CATEGORICAL FORECASTS: VIS

Ceiling height forecasts for each specific 3 hour forecast
time from 6 to 48 hours following 0000 or 1200 UTC are made using
five categories of ceiling height. The digital code for each forecast
ceiling height category appears in the accompanying table. These
forecast codes are found under the appropriate forecast time header.

Forecasts for those potential conditions causing obstructions
to vision are made in terms of three categories for each specific
3 hour forecast time from 6 to 48 hours following 0000 or 1200
UTC. The single letter code for each category appears in the accompanying
table. These forecast codes are found under the appropriate forecast
time. Reduced visibilities caused exclusively by heavy precipitation
events are not predicted.